Multiple input, multiple output (MIMO) systems refer to communication systems that have multiple transmission and multiple reception antennas at both enhanced Node B (eNB) (or base station (BS), Node B (NB), communications controller, and so forth) and User Equipment (UE) (or mobile station (MS), terminal, user, relay, subscriber, subscriber equipment, and so on). Such MIMO systems can achieve better channel utilization and better overall performance. The Third Generation Partnership Project (3GPP) E-UTRA standards specify MIMO schemes for use by E-UTRA UEs and eNBs. Single-cell enhanced Multi-User MIMO (MU-MIMO) has been identified as an important technique for LTE Advanced (LTE-A) to improve system performance. In LTE Rel-8, Single-User MIMO (SU-MIMO) and MU-MIMO are supported by different transmission modes which are configured semi-statically by higher layer. In LTE Rel-9 and LTE Rel-10, transparent MU-MIMO can be supported.
In a typical Multi-User Multiple-Input Multiple-Output (MU-MIMO) system, a transmitter transmits a MU-MIMO signal, which comprises multiple signals that are addressed to multiple respective receivers. Each of the signals is precoded with a respective precoding scheme, and the signals are spatially-multiplexed and transmitted in the same time-frequency slot, therefore a signal to one receiver can cause more interference to another.